Centrifugal separation of wax and oil



May 24, 1960 J. VAN DYCK FEAR 2,937,985

CENTRIFUGAL SEPARATION OF WAX AND OIL Filed May 31, 1957 2 Sheets-Sheet1 IN VEN TOR. JAMES VAN DYCK FEAR wsebio. yf M ATTORNEY May 24, 1960 J.VAN DYCK FEAR 2,937,985

CENTRIFUGAL SEPARATION OF WAX AND OIL Filed May 31, 1957 2 Sheets-Sheet2 Waxy O l Fig. 2

0hi|ler centrifuge 2o I I I 6 28 2 I I 23 .J L waxcuke l m Oil-Solventso ve Effluent 1 27 INVENTOR.

JAMES VAN DYCK FEAR QAgko. sdawflh ATTORNEY United States Patent C)CENTRIFUGAL SEPARATION or WAX AND OIL James Van Dyck Fear, Media, Pa.,assignor to Sun Oil Company, Philadelphia, Pa., a corporation of NewJersey Filed May 31, 1957, Ser. No. 662,866

4 Claims. (Cl. 208-33) This invention relates to the separation of waxand oil and more particularly is directed to a continuous process fordewaxing oils or deoiling waxes utilizing a rotating centrifugal wheel.

The use of centrifuges for effecting separation of wax and oil from eachother has long been known. In processes of this type the waxy chargeusually is admixed with fresh solvent which is capable of dissolving theoil but is an anti-solvent for the wax, and the mixture is chilled to asuitable dewaxing temperature to precipitate the wax and then is fed tothe centrifuge wherein the wax is caused to separate from the oil andsolvent. The oil-solvent stream withdrawn from the centrifuge isdistilled to recover the solvent which is then re-used.

The present invention is directed to an improvement in the centrifugalseparation of wax from oil, which permits effective separation whileminimizing the amount of solvent required in the system. In the processprovided by the invention, addition of fresh solvent to the waxy chargeis avoided and the total amount of fresh solvent fed to the system isutilized as wash liquid for washing the separated wax crystals.

The process according to the invention utilizes a rotating centrifugalwheel in which both the separation of wax from oil and washing of thewax crystals is effected. The waxy hydrocarbon charge, instead of beingdiluted with fresh solvent, is admixed with a portion of the oilsolventefiiuent obtained from the wheel. The resulting mixture is continuouslyintroduced at a dewaxing temperature into the interior of the wheel at alocus intermediate its hub and periphery. Fresh dewaxing solvent, havinga density less than that of the wax and chilled to the dewaxingtemperature, is continuously introduced into the wheel at a locusbetween its periphery and the point of introduction of the chargemixture. The centrifugal force within the wheel causes the oil to flowtoward its hub and the wax to flow toward the periphery countercurrentto the wash solvent. A stream of wax is withdrawn from adjacent theperiphery of the wheel while the oil-solvent mixture is continuouslywithdrawn as efiluent from adjacent the hub. A portion of this effluentis returned for admixture with the waxy charge.

The following more detailed description of the invention is made withreference to the accompanying drawings in which:

Fig. l is a fragmentary cross-sectional view of a centrifugal wheel of atype useful in practicing the invention; and

Fig. 2 is a schematic flowsheet illustrating an embodiment of thepresent process.

Referring to Fig. 1, centrifugal wheel 1 and its hub 2 are adapted to berotated by a suitable driving means, not shown. A mixture of a waxycharge oil and oilsolvent effiuent previously withdrawn from wheel 1 iscontinuously admitted to the interior of the rotating wheel underpressure at a suitable dewaxing temperature, for example, at 20 F.,through inlet line 7 and pasice sage 8 to an intermediate point betweenthe hub and periphery of the wheel. An oil solvent, which has a lowerdensity than the wax and which has low solubility for the wax, such as amixture of 65% methyl ethyl ketone and 35% propane, is continuouslyintroduced under pressure and at the dewaxing temperature to theinterior of the wheel near the periphery through inlet line 3, inletpassage 4 and distributor 5. Under the influence of the centrifugalforce generated in wheel 1, the solvent flows through perforated baffles6 towards the hub of the wheel, while the wax in the charge introducedthrough passage 8 passes toward the periphery making countercurerntcontact on its way with the solvent. From the outlet of passage 8, oildissolved in solvent flows inwardly toward the hub and is removedthrough passage 9 and annulus 10. The wax, washed substantially free ofoil, is collected at the periphery of wheel 1 and, being of plasticcharacter, can be forced continuously therefrom through passage 11 andannulus 12. Suitable means, such as a back pressure valve on theoil-solvent efiluent line (not shown), should be provided to insure thatthere will be at all times sufiicient pressure in the interior of wheel1 to force the wax cake through the passages provided therefor.

Fig. 2 schematically illustrates a preferred manner of practicing theinvention, wherein two portions of the oilsolvent efiluent are mixed atseparate points with the wax-bearing charge prior to centrifuging.Numeral 29 illustrates the centrifugal wheel shown in more detail inFig. 1. Waxy charge oil enters the system through line 21 andis sent tochiller 22. Before'entering the chiller it preferably is admixed withonly a part of the total efilnent which is recycled from centrifuge 20through line 23. This first portion of effluent is sent through line 24for admixture with the charge oil, and the amount used should besufficient to prevent the material passing through the chiller frombecoming so viscous that excessive pumping pressure and inadequate heattransfer'rates result. Following the chilling step, the remainder of therecycled eflluent is added to the charge via line 25. The temperature towhich the mixture is cooled in chiller 22 depends upon the dewaxingtempearture desired and the temperature and amount of efiluent addedthrough line 25. Usually this efliuent will have a temperature somewhatabove the desired dewaxing temperature due to frictional effects withinthe centrifuge and heat transfer through the flow lines, andconsequently it generally will be necessary to cool in chiller 22somewhat below the dewaxing temperature so that the final mixture fed tocentrifuge 20 will be at the desired temperature level.

The cold charge mixture enters the centrifuge through line 26 and isintroduced into its interior at a locus as described in connection withFig. 1. Wash solvent is admitted through line 27 and wax cake iswithdrawn via line 28, also as described with reference to Fig. 1. Theoil product in admixture with solvent is withdrawn through line 29 andsent to a distillation zone (not shown) for recovery of the solvent forre-use.

In practicing the invention any of the known dewaxing solvents whichhave a density substantially less than that of the wax in the chargestock may be used. It is preferred to employ as the solvent a mixturecomprising a good anti-solvent for wax, such as a ketone, and a good oilsolvent such as an aliphatic or aromatic hydrocarbon. A prefered solventmixture comprises methyl ethyl ketone and a saturated hydrocarbon of theC -C range such as propane, butane, pentane, isopentane or a hexane.Particularly satisfactory proportions of the solvent components arewithin the range of 60-70% of the ketone and 30-40% of the saturatedhydrocarbon.

The following example, in which parts and percentages are by volume,specifically illustrates the present process carried out in the mannerdepicted in Fig. 2. Thecharge stock is a solvent refined distillate oilderived from a paraffinic crude and typically having a viscosity of 150S.U.S. at 100 F. and a wax content of 20%. The charge stock is fed tothe system at a rate of 100 parts per unit of time and, prior tochilling, is admixed with a portion of cold recycled efliuent from thecentrifuge comprising 50 parts of dewaxed oil and 150 parts of solvent.The mixture is chilled to a temperature somewhat below -15 F. and isthen admixed with a second portion of recycled effluent comprising 50parts of oil and 150 parts of solvent having a temperature somewhatabove 15 F. The resulting mixture, which has a temperature of about 15F., is continuously introduced to the centrifuge at a rate of 500 partsper unit of time. Fresh solvent is introduced into the centrifugal wheelnear its periphery at a temperature of about 15 F. and a rate of 300parts per unit of time. Under these conditions the stream of wax cakewithdrawn from the centrifuge per unit of time is composed of 20 partsof wax, 1 part of oil and 63 parts of solvent. This material is sent toa distillation unit for recovery of the solvent. The oil-solventefliuent stream is removed from the centirfuge at the rate of 716 partsper unit of time and 400 parts of this are recycled in the mannerpreviously described. The remainder, comprising 79 parts of dewaxed oiland 237 parts of solvent, is sent to a second distillation unit forrecovery of the solvent. The resulting dewaxed oil has a pour point ofabout F.

The following conventional manner of carying out a dewaxing operationutilizing a centrifuge is given for purposes of comparison with theforegoing operation. In the conventional operation, 100 parts of thecharge stock is admixed with 200 parts of fresh solvent and the mixtureis chilled to l5 F. and then fed into the centrifuge. Wash solvent isintroduced into the centrifuge near its periphery at a temperature ofabout -15 F. and a rate of 100 parts per unit of time. The stream of waxcake withdrawn from the centrifuge comprises 20 parts of wax, 5 parts ofoil and 75 parts of solvent, while the filtrate effiuent streamcomprises 75 parts of oil and 225 parts of solvent. These products areseparately distilled to recover the solvent.

The foregoing comparative operations are based upon using the same totalamounts of fresh solvent, namely, 300 parts per unit of time. Theconventional operation yields a wax product having 5 parts of oil foreach 20 parts of wax, while operation according to the invention yieldsa product having only 1 part of oil to 20 parts of wax. Thus, practiceof the invention permits a substantially more effective separation ofthe oil and wax.

Alternatively, in operating according to the invention, the total amountof fresh solvent used can be reduced considerably while securing thesame degree of separation between the wax and oil as is obtained in theconventional manner of operation employing a larger amount of freshsolvent.

I claim:

1. Process for separating wax from oil by means of a rotatingcentrifugal wheel which comprises admixing an undiluted hydrocarboncharge consisting of oil and wax with hereinafter specified efiluentfrom the wheel, continuously introducing the mixture at a dewaxingtemperature into the interior of the wheel at a locus intermediate itshub and periphery, continuously introducing a chilled dewaxing solventhaving low solubility for wax and a density less than that of the waxinto the interior of the wheel at a locus between the first-mentionedlocus and the periphery, said solvent being the sole amount of solventemployed in the process, withdrawing wax from the wheel at a locusadjacent its periphery via a conduit connecting the periphery with anoutlet adjacent to the hub, withdrawing from the wheel adjacent its hubeffluent comprising oil and solvent, and returning a major portion ofsaid effluent comprising oil and solvent for admixture with the charge.

2. Process according to claim 1 wherein said solvent comprises a mixtureof methyl ethyl ketone and a saturated hydrocarbon of the C -C range.

3. Process for separating wax from oil by means of a rotatingcentrifugal wheel which comprises admixing an undiluted hydrocarboncharge consisting of oil and wax with a first portion of hereinafterspecified efiluent' from the wheel, chilling the mixture to a dewaxingtemperature, admixing the chilled mixture with a second portion of saidefiluent, continuously introducing the resulting mixture into theinterior of the wheel at a locus intermediate its hub and periphery,continuously introducing a chilled dewaxing solvent having lowsolubility for wax and a density less than that of the wax into theinterior of the wheel at a locus between the first-mentioned locus andthe periphery, said solvent being the sole amount of solvent employed inthe process withdrawing wax from the wheel at a locus adjacent itsperiphery via a conduit connecting the periphery with an outlet adjacentto the hub, withdrawing from the wheel adjacent its hub efiiuentcomprising oil and solvent, and returning a major amount of saideffluent comprising oil and solvent as said first and second portionsfor admixture with the charge as herein specified.

4. Process according to claim 3 wherein said solvent comprises a mixtureof methyl ethyl ketone and a saturated hydrocarbon of the C -C range.

References Cited in the file of this patent UNITED STATES PATENTS

1. PROCESS FOR SEPARATING WAX FROM OIL BY MEANS OF A ROTATINGCENTRIFUGAL WHEEL WHICH COMPRISES ADMIXING AN UNDILUTED HYDROCARBONCHARGE CONSISTING OF OIL AND WAX WITH HEREINAFTER SPECIFIED EFFUENT FROMTHE WHEEL, CONTINUOUSLY INTRODUCING THE MIXTURE AT A DEWAXINGTEMPERATURE INTO THE INTERIOR OF THE WHEEL AT A LOCUS INTERMEDIATE ITSHUB AND PERIPHERY, CONTINUOUSLY INTRODUCING A CHILLED DEWAXING SOLVENTHAVING LOW SOLUBILITY FOR WAX AND A DENSITY LESS THAN THAT OF THE WAXINTO THE INTERIOR OF THE WHEEL AT A LOCUS BETWEEN THE FIRST-MENTIONEDLOCUS AND THE PERIPHERY, SAID SOLVENT BEING THE SOLE AMOUNT OF SOLVENTEMPLOYED IN THE PROCESS, WITHDRAWING WAX FROM THE WHEEL AT A LOCUSADJACENT ITS PERIPHERY VIA A CONDUIT CONNECTING THE PERIPHERY WITH ANOUTLET ADJACENT TO THE HUB, WITHDRAWING FROM THE WHEEL ADJACENT ITS HUBEFFLUENT COMPRISING OIL AND SOLVENT, AND RETURNING A MAJOR PORTION OFSAID EFFLUENT COMPRISING OIL AND SOLVENT FOR ADMIXTURE WITH THE CHARGE.